c-family: Fix up shorten_compare for decimal vs. non-decimal float comparison [PR104510]

The comment in shorten_compare says:
  /* If either arg is decimal float and the other is float, fail.  */
but the callers of shorten_compare don't expect anything like failure
as a possibility from the function, callers require that the function
promotes the operands to the same type, whether the original selected
*restype_ptr one or some shortened.
So, if we choose not to shorten, we should still promote to the original
*restype_ptr.

2022-02-16  Jakub Jelinek  <jakub@redhat.com>

	PR c/104510
	* c-common.cc (shorten_compare): Convert original arguments to
	the original *restype_ptr when mixing binary and decimal float.

	* gcc.dg/dfp/pr104510.c: New test.

diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index bf0749b..7203d76 100644 (file)
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -3174,7 +3174,11 @@ shorten_compare (location_t loc, tree *op0_ptr, tree *op1_ptr,
   else if (real1 && real2
           && (DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (primop0)))
               || DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (primop1)))))
-    return NULL_TREE;
+    {
+      type = *restype_ptr;
+      primop0 = op0;
+      primop1 = op1;
+    }
 
   else if (real1 && real2
           && (TYPE_PRECISION (TREE_TYPE (primop0))

diff --git a/gcc/testsuite/gcc.dg/dfp/pr104510.c b/gcc/testsuite/gcc.dg/dfp/pr104510.c
new file mode 100644 (file)
index 0000000..85f4e97
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/pr104510.c
@@ -0,0 +1,12 @@
+/* PR c/104510 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+float f;
+_Decimal64 d;
+
+int
+foo (void)
+{
+  return d > (_Decimal32) (_Decimal64) f;
+}